(1) Field of the Invention
This invention relates generally to the measurement of the tension in elongated flexible material such as string, cord, wire, cable and the like. More particularly, the present invention is directed to compact devices for measuring the tension of the strings of a sports racquet. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in measuring the tension in the strings of a tennis racquet. A number of compact devices have been proposed for measuring the tension of the strings of a tennis racquet or other sport racquet. For example, Walker U.S. Pat. No. 4,309,910 discloses a racquet string tension tester which employs an elongated hollow handle having a cylindrical block rotatably mounted in a circular opening at the front of the handle. A torsion spring mounted within the handle extends between the cylindrical block and the rear of the handle. V-shaped notches are disposed at the outer end of the cylindrical block for firmly engaging the strings to be tested. The handle is manually rotated for sensing the tension of the strings of a racquet.
Cummins et al U.S. Pat. No. 3,831,442 discloses a string tension measuring device having an integral form which includes a handle, a string engaging portion and a resilient portion which joins the handle and the string engaging portion. The string engaging portion has a calibrated scale and a reference mark. The handle has an index mark which is positioned so that when the handle is twisted relative to the engaged portion of the string, the tension is indicated on the scale by the index mark when the reference mark aligns with the string being tested.
The devices disclosed in the above-discussed patents operate on substantially the same principle. A torque is applied to a string to cause deflection thereof in the plane of the racquet. The amount of deflection corresponds to the tension of the string. Because the racquet and strings are deflected in the plane of the racquet, the deflected string necessarily slides across the adjacent cross-strings. The sliding across other strings during displacement of the string under test introduces a significant friction force which effects the measurement and thus limits the accuracy of the measurement. In addition, there is necessarily friction between the moving parts of the prior devices and such friction can be a significant source of error in the tension measurement. Moreover, in the devices disclosed in U.S. Pat. Nos. 3,831,442 and 4,309,910, the tension is measured by manual application of a torque. Consequently, the quality of the measurement is also a function of the skill of the tester.